Straw rubbing machine has many problems such as high energy consumption, low efficiency and high production cost, which seriously restrict the promotion and development of rubbing machine. In order to achieve efficient rubbing, the relationship between the hammer of rubbing machine structure parameters and rubbing efficiency was studied. From the perspective of aerodynamics, the relationship between rubbing machine cavity flow field structure and material movement in T type structure of hammer excitation was analyzed. And then the T type hammer excitation rubbing machine cavity flow field pressure distribution and velocity field distribution were obtained by using computational fluid dynamics (CFD) technology. The simulation results showed that the rubbing machine cavity air axial velocity gradient was large, and the transport characteristics of suspension circulation layer were high. The axial air velocity was increased gradually, and the flow field velocity gradient was obvious. Validation test was designed, and the simulation results of wind speed and test values were compared. Results showed that the simulation results were in agreement with the experimental values, and the maximum relative error of the two was about 8%. The results also showed that the numerical simulation of the flow field in the type 9R-40 straw rubbing machine was reasonable which can correctly indicate the distribution of flow field when the machine was no-load. The flow structure inside the machine can provide a new direction to optimize the rubbing, and also provide a theoretical basis for the optimization design of mechanical rubbing.